It is up to you to decide where to draw the ethical line, how exactly you want to use this tool in influencing others to help achieve your goals. Personally, don't send me a crisp dollar bill, I know you don't really care about me and I see it as intentional manipulation. On the other hand, keep the free samples coming in the food court. I think you believe in your product and just want to offer me a tasty treat that might just convince me to take a seat.